Syntheses, Structures, and Reactivities of Heterobimetallic Bridging Dinitrogen Complexes Containing Group 6 and Group 4 or 5 Transition Metals¹

A series of heterobimetallic dinitrogen complexes containing group 6 and group 4 or 5 transition metals were synthesized by the reaction of the tungsten or molybdenum dinitrogen complexes cis -[W(N 2 ) 2 (PMe 2 Ph) 4 ] ( 1 ) and trans -[M(N 2 ) 2 (dppe) 2 ] ( 2 ) (M = W, Mo) with group 4 or group 5 compounds such as [CpTiCl 3 ], [Cp 2 M‘Cl 2 ] (M‘ = Ti, Zr, Hf), or [Cp‘M‘Cl 4 ] (Cp‘ = Cp, Cp*; M‘ = Nb, Ta). Crystallographic studies of the complexes thus obtained including [WCl(PMe 2 Ph) 4 (μ-N 2 )TiCpCl 2 ] and [WCl(PMe 2 Ph) 4 (μ-N 2 )NbCpCl 3 ] revealed that the M−N−N−M‘ core is essentially linear, and the N−N bond is regarded to have the formal bond order of 2. Several μ-N 2 complexes with methyl ligands at the group 4 or 5 metal center were also obtained through the reaction of dinitrogen complexes 1 and 2a (M = W) with the methyl complexes [Cp 2 ZrMeCl], [TaMe 3 Cl 2 ], and [NbMe 2 Cl 3 ]. The reaction of the complex [WCl(dppe) 2 (μ-N 2 )TiCpCl 2 ] with Li 2 S 5 afforded the η 2 -pentasulfido complex [WCl(dppe) 2 (μ-N 2 )TiCpS 5 ], where the η 2 -S 5 ligand forms a six-membered chelate ring with the chair conformation. Protonation of the μ-N 2 complexes having PMe 2 Ph ligands gave NH 3 in moderate yield, concurrent with the formation of a small amount of NH 2 NH 2 .